Signaling of coding tools for encoding a video component as monochrome video

ABSTRACT

A method of video decoding performed in a video decoder is disclosed. A syntax element can be received from a bitstream of a coded video that indicates whether a sequence of pictures are monochrome or include three color components that are coded separately. By inferring a value of a syntax element, a coding tool can be disabled when the syntax element indicates that the sequence of pictures are monochrome or include three color components that are coded separately. The coding tool uses multiple color components of a picture as input or depends on a chroma component of a picture. Examples of the disabled coding tools can include joint coding of chroma residuals, active color transform (ACT), or block-based delta pulse code modulation (BDPCM) for chroma component.

INCORPORATION BY REFERENCE

This application is a continuation of application Ser. No. 17/072,980,filed Oct. 16, 2020, which claims the benefit of priority to U.S.Provisional Application No. 62/924,674, “Signaling of Video Coding Toolsfor the Encoding of a Video Component as Monochrome Video” filed on Oct.22, 2019, which are incorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction besides DCprediction. However, some newer video compression technologies includetechniques that attempt, from, for example, surrounding sample dataand/or metadata obtained during the encoding/decoding of spatiallyneighboring, and preceding in decoding order, blocks of data. Suchtechniques are henceforth called “intra prediction” techniques. Notethat in at least some cases, intra prediction is only using referencedata from the current picture under reconstruction and not fromreference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

Referring to FIG. 1A, depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves cansometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

The intra prediction modes used in HEVC are illustrated in FIG. 1B. InHEVC, there are total 35 intra prediction modes, among which mode 10 ishorizontal mode, mode 26 is vertical mode, and mode 2, mode 18 and mode34 are diagonal modes. The intra prediction modes are signalled by threemost probable modes (MPMs) and 32 remaining modes.

FIG. 1C illustrates the intra prediction modes used in VVC. In VVC,there are total 95 intra prediction modes as shown in FIG. 1C, wheremode 18 is the horizontal mode, mode 50 is the vertical mode, and mode2, mode 34 and mode 66 are diagonal modes. Modes −1˜−14 and Modes 67˜80are called Wide-Angle Intra Prediction (WAIP) modes.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingMPMs, and similar techniques. In all cases, however, there can becertain directions that are statistically less likely to occur in videocontent than certain other directions. As the goal of video compressionis the reduction of redundancy, those less likely directions will, in awell working video coding technology, be represented by a larger numberof bits than more likely directions.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate) of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 1D, a current block (110) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (102 through 106, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using. The order of forming acandidate list may be A0→B0→B1→A1→B2.

SUMMARY

Aspects of the disclosure provide a method of video decoding performedin a video decoder. A syntax element can be received from a bitstream ofa coded video that indicates whether a sequence of pictures aremonochrome or include three color components that are coded separately.By inferring a value of a syntax element, a coding tool can be disabledwhen the syntax element indicates that the sequence of pictures aremonochrome or include three color components that are coded separately.The coding tool uses multiple color components of a picture as input ordepends on a chroma component of a picture.

In an embodiment, the disabled coding tool is one of a coding tool ofjoint coding of chroma residuals, active color transform (ACT), orblock-based delta pulse code modulation (BDPCM) for chroma component.

In an embodiment, the value of the syntax element indicating whetherjoint coding of chroma residuals is enabled is inferred to be equal tozero. In an embodiment, the value of the syntax element indicatingwhether ACT is enabled can be inferred to be equal to zero. In anembodiment, the value of the syntax element indicating whether BDPCM forchroma component is enabled can be inferred to be equal to zero.

In an embodiment, a value of a variable is determined to be zero whenthe syntax element indicates that the sequence of pictures aremonochrome or include three color components that are coded separately.The variable indicates a chroma array type of the sequence of pictures.In response to determining the value of the variable to be zero, thevalue of one of the following syntax elements can inferred to be equalto zero: a syntax element indicating whether joint coding of chromaresiduals is enabled, a syntax element indicating whether ACT isenabled, or a syntax element indicating whether BDPCM for chromacomponent is enabled.

In some embodiments, in response to determining the sequence of picturesare not monochrome and include three color components that are not codedseparately, a syntax element indicating whether joint coding of chromaresiduals is enabled can be received; a syntax element indicatingwhether ACT is enabled can be received; or a syntax element indicatingwhether BDPCM for chroma component is enabled can be received.

In an embodiment, in response to determining the sequence of picturesare not monochrome and include three color components that are not codedseparately, a value of a variable indicating a chroma array type of thesequence of pictures can be determined. One of the following syntaxelements can be received when the value of the variable is determined tobe non-zero: a syntax element indicating whether joint coding of chromaresiduals is enabled, a syntax element indicating whether ACT isenabled, or a syntax element indicating whether BDPCM for chromacomponent is enabled.

In an embodiment, a value of a variable indicating a chroma array typeof the sequence of pictures can be determined when it is determined thatthe sequence of pictures are not monochrome and include three colorcomponents that are not coded separately. A syntax element indicatingwhether BDPCM for chroma component is enabled can be received when thevalue of the variable is determined to be non-zero, and when a losslessmode is enabled for the sequence of pictures.

Aspects of the disclosure provide an apparatus of video decodingcomprising circuitry. The circuitry can be configured to receive asyntax element from a bitstream of a coded video. The syntax elementindicates whether a sequence of pictures are monochrome or include threecolor components that are coded separately. The circuitry can be furtherconfigured to infer a value of a syntax element to disable a coding toolthat uses multiple color components of a picture as input or depends ona chroma component of a picture when the syntax element indicates thatthe sequence of pictures are monochrome or include three colorcomponents that are coded separately.

Aspects of the disclosure provide a non-transitory computer-readablemedium storing instructions that, when executed by a processor, causethe processor to perform the method of video decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1A is a schematic illustration of an exemplary subset of intraprediction modes;

FIG. 1B is an illustration of exemplary intra prediction directions.

FIG. 1C is an illustration of exemplary intra prediction directions.

FIG. 1D is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 8 is an illustration of an embodiment of a process performed by adecoder.

FIG. 9 is an illustration of an embodiment of another process performedby a decoder.

FIG. 10 is a schematic illustration of a computer system in accordancewith an embodiment of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

I. Video Encoder and Decoder Systems

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313), that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks including sample values that canbe input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (452) has generated to the outputsample information as provided by the scaler/inverse transform unit(451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4. Brieflyreferring also to FIG. 4, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415), andparser (420) may not be fully implemented in the local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (503), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

II. Separately Coding Video Color Components

Video coding technologies typically assume that a to-be-encoded videosequence has multiple color planes (e.g., one luma component and twochroma components). By employing certain coding tools, the color planescan be encoded jointly. For example, luma and chroma components of asame picture may share a same partitioning tree. Coded luma and chromacomponents can be organized into a same CU. Coding of chroma componentsmay reference pixel values or residual values of a luma component forprediction (e.g., cross component linear model (CCLM)). A processingstep may use three luma and chroma components as input (e.g., activecolor transform (ACT)). Or, two chroma components can be coded jointly(e.g., joint coding of chroma residuals (JCCR)).

However, in some applications, either a video is monochrome, or multiplecolor planes of a video are required to be encoded independently. Forexample, three color components of a video having a 4:4:4 chroma formatmay be required to be coded separately and independently. For example,each color component of the video is treated as a monochrome video.There is no dependency between those color components while the videobeing coded. Coding tools depending on multiple components (e.g., ACTand JCCR) or operating on chroma components (e.g., block-based delta (ordifferential) pulse code modulation (BDPCM)) are not employed. Coding ofthe video is based on monochrome coding tools operating on lumacomponent.

To support coding of videos with different chroma formats and videosincluding one or more monochrome components, in some embodiments, twosyntax elements are defined as shown in Table 1.

TABLE 1 chroma_format_idc separate_colour_plane_flag Chroma format 0 0Monochrome 1 0 4:2:0 2 0 4:2:2 3 0 4:4:4 3 1 4:4:4

The syntax element, chroma_format_idc, provides an index to multiplechroma formats. The defined chroma formats correspond to differentchroma component sampling structures. Specifically, in monochromesampling, there is only one sample array, which is nominally considereda luma array. In 4:2:0 sampling, each of the two chroma arrays can havehalf the height and half the width of the luma array. In 4:2:2 sampling,each of the two chroma arrays can have the same height and half thewidth of the luma array. For convenience of notation and terminology inthis disclosure, the variables and terms associated with these arraysare referred to as luma and chroma. The two chroma arrays are referredto as Cb and Cr regardless of the actual color representation method inuse. The actual color representation method in use can be indicated insyntax transmitted in a bitstream.

The syntax element, separate_colour_plane_flag, indicates whether colorcomponents of a video sequence are required to be coded separately. Forexample, separate_colour_plane_flag equal to 1 specifies that the threecolor components of the 4:4:4 chroma format can be coded separately.separate_colour_plane_flag equal to 0 specifies that the colorcomponents are not coded separately. When separate_colour_plane_flag isnot present, it is inferred to be equal to 0.

When separate_colour_plane_flag is equal to 1, the coded pictureconsists of three separate components, each of which consists of codedsamples of one color plane (e.g., Y, Cb, or Cr) and uses monochromecoding syntax. In this case, each color plane is associated with aspecific colour_plane_id value. There is no dependency in decodingprocesses between the color planes having different colour_plane_idvalues. For example, the decoding process of a monochrome picture withone value of colour_plane_id does not use any data from monochromepictures having different values of colour_plane_id for inter or intraprediction.

In 4:4:4 sampling, each of the two chroma arrays has the same height andwidth as the luma array, and depending on the value ofseparate_colour_plane_flag, the following can apply. Ifseparate_colour_plane_flag is equal to 0, the three color planes are notseparately processed as monochrome sampled pictures. Otherwise(separate_colour_plane_flag is equal to 1), the three color planes areseparately processed as monochrome sampled pictures.

In an example, the syntax elements, chroma_format_idc andseparate_colour_plane_flag, are signaled in a sequence parameter set(SPS) as shown in Table 2. At row 11 of Table 2, chroma_format_idc issignaled. At row 12, whether chroma_forma_idc indicates the 4:4:4 chromaformat sampling structure is verified. At row 13, when thechroma_format_idc has a value of 3, separate_colour_plane_flag issignaled to indicate whether components of a video sequence referencingthe SPS of Table 2 are coded separately.

When a video is a monochrome video or is required to encode each colorcomponent of the video as if each component is monochrome, joint colorplane coding tools or chroma component based coding tools are notapplicable and can be disabled. However, as shown in Table 2, severalsyntax elements controlling those inapplicable coding tools are signaledindependently from whether separate encoding of color components isenabled (or required). As a result, some coding tools inapplicable tomonochrome videos can still be enabled when separate encoding ofdifferent color planes as monochrome videos is employed for a currentvideo, causing undesirable conflicts.

Specifically, at row 86 of Table 2, a syntax element,sps_joint_cbcr_enabled_flag, is signaled without dependency on thesperate_colour_plane_flag signaled at row 13. Thesps_joint_cbcr_enabled_flag can indicate whether the joint coding ofchroma residuals (JCCR) tool is enabled for coding a video. As twochroma components of a CU are jointly coded, the JCCR coding tool is nota monochrome coding tool. The sps_joint_cbcr_enabled_flag equal to 0specifies that the joint coding of chroma residuals is disabled. Thesps_joint_cbcr_enabled_flag equal to 1 specifies that the joint codingof chroma residuals is enabled.

At rows 104-105, when BDPCM is enabled and the chroma format is 4:4:4, asyntax element, sps_bdpcm_chroma_enabled_flag, is signaled withoutdependency on the sperate_colour_plane_flag signaled at row 13. Thesperate_colour_plane_flag can indicate whether the tool of BDPCM forchroma is enabled for coding a video. The BDPCM for chroma is a codingtool applied to chroma component, and thus can be disabled if the videois monochrome, or is required to encode each color component of thevideo as if each component is monochrome.

Regarding the semantics, sps_bdpcm_chroma_enabled_flag equal to 1specifies that intra_bdpcm_chroma_flag may be present in coding unitsyntax for intra coding units. sps_bdpcm_chroma_enabled_flag equal to 0specifies that intra_bdpcm_chroma_flag is not present in the coding unitsyntax for intra coding units. When not present, the value ofsps_bdpcm_chroma_enabled_flag is inferred to be equal to 0.Intra_bdpcm_chroma_flag equal to 1 specifies that BDPCM is applied tocurrent chroma coding blocks, i.e. the transform is skipped, the intrachroma prediction mode is specified by intra_bdpcm_chroma_dir_flag.intra_bdpcm_chroma_flag equal to 0 specifies that BDPCM is not appliedto the current chroma coding blocks. When intra_bdpcm_chroma_flag is notpresent it is inferred to be equal to 0.

At rows 142 and 144 of Table 2, when the chroma format is 4:4:4, asyntax element, sps_act_enabled_flag, is signaled without dependency onthe sperate_colour_plane_flag signaled at row 13. Thesps_act_enabled_flag can indicate whether the ACT tool is enabled forcoding a video. For example, a color format (e.g., RGB) in an originalcolor space can have high correlations among three color components. Byperforming a color space conversion, the color format can be convertedfrom the original color space to a target color space to reduceredundancy among the three color components. For example, in HEVC orVCC, the ACT can be performed in spatial residual domain to convertresidual blocks from RGB color space to YCgCo color space. The residualblocks of three components are used as input. Thus, ACT is notapplicable to a monochrome video or a video having color componentsprocessed separately.

Regarding the semantics, sps_act_enabled_flag specifies that whetheradaptive color transform is enabled. If sps_act_enabled_flag is equal to1, adaptive color transform may be used and the flag cu_act_enabled_flagmay be present in the coding unit syntax. If sps_act_enabled_flag isequal to 0, adaptive color transform is not used and cu_act_enabled_flagis not present in the coding unit syntax. When sps_act_enabled_flag isnot present, it is inferred to be equal to 0.

TABLE 2 Descriptor  1 sps_parameter_set_rbsp( ) {  2 sps_decoding_parameter_set_id u(4)  3  sps_video_parameter_set_id u(4) 4  sps_max_sub_layers_minus1 u(3)  5  sps_reserved_zero_4bits u(4)  6 sps_ptl_dpb_hrd_params_present_flag u(1)  7  if(sps_dpb_hrd_params_present_flag )  8   profile_tier_level( 1,sps_max_sub_layers_minus1 )  9  gdr_enabled_flag u(1)  10 sps_seq_parameter_set_id u(4)    11 **  chroma_format_idc u(2)    12 ** if( chroma_format_idc = = 3)    13 **   separate_colour_plane_flag u(1) 14  ref_pic_resampling_enabled_flag u(1)  15  sps_seq_parameter_set_idue(v)  16  chroma_format_idc ue(v)  17  pic_width_max_in_luma_samplesue(v)  18  pic_height_max_in_luma_samples ue(v)  19 sps_log2_ctu_size_minus5 u(2)  20  subpics_present_flag u(1)  21  sps_num_subpics_minus1 u(8)  22   for( i = 0; i <=sps_num_subpics_minusI; i++ ) {  23    subpic_ctu_top_left_x[ i ] u(v) 24    subpic_ctu_top_left_y[ i ] u(v)  25    subpic_width_minus1[ i ]u(v)  26    subpic_height_minus1[ i ] u(v)  27   subpic_treated_as_pic_flag[ i ] u(1)  28   loop_filter_across_subpic_enabled_flag[ i ] u(1)  29   }  30  }  31 sps_subpic_id_present_flag u(1)  32  if( sps_subpics_id_present_flag ){  33   sps_subpic_id_signalling_present_flag u(1)  34   if(sps_subpics_id_signalling_present_flag ) {  35   sps_subpic_id_len_minus1 ue(v)  36    for( i = 0; i <=sps_num_subpics_minus1; i++ )  37     sps_subpic_id[ i ] u(v)  38   } 39  }  40  bit_depth_minus8 ue(v)  41  min_qp_prime_ts_minus4 ue(v)  42 sps_weighted_pred_flag u(1)  43  sps_weighted_bipred_flag u(1)  44 log2_max_pic_order_cnt_lsb_minus4 u(v)  45  sps_poc_msb_flag u(1)  46 if( sps_poc_msb_flag )  47   poc_msb_len_minus1 ue(v)  48  if(sps_max_sub_layers_minus1 > 0 )  49   sps_sub_layer_dpb_params_flag u(1) 50  if( sps_ptl_dpb_hrd_params_present_flag )  51   dpb_parameters( 0,sps_max_sub_layers_minus1, sps_sub_layer_dpb_params_flag )  52 long_term_ref_pics_flag u(1)  53  inter_layer_ref_pics_present_flagu(1)  54  sps_idr_rpl_present_flag u(1)  55  rpl1_same_as_rpl0_flag u(1) 56  for( i = 0; i < !rpl1_same_as_rpl0_flag ? 2: 1; i++ ) {  57  num_ref_pic_lists_in_sps[ i ] ue(v)  58   for( j =0; j <num_ref_pic_lists_in_sps[ i ]; j++)  59    ref_pic_list_struct( i, j ) 60  }  61  if( ChromaArrayType != 0 )  62   qtbtt_dual_tree_intra_flagu(1)  63  log2_min_luma_coding_block_size_minus2 ue(v)  64 partition_constraints_override_enabled_flag u(1)  65 sps_log2_diff_min_qt_min_cb_intra_slice_luma ue(v)  66 sps_log2_diff_min_qt_min_cb_inter_slice ue(v)  67 sps_max_mtt_hierarchy_depth_inter_slice ue(v)  68 sps_max_mtt_hierarchy_depth_intra_slice_luma ue(v)  69  if(sps_max_mtt_hierarchy_depth_intra_slice_luma != 0 ) {  70  sps_log2_diff_max_bt_min_qt_intra_slice_luma ue(v)  71  sps_log2_diff_max_tt_min_qt_intra_slice_luma ue(v)  72  }  73  if(sps_max_mtt_hierarchy_depth_inter_slice != 0 ) {  74  sps_log2_diff_max_bt_min_qt_inter_slice ue(v)  75  sps_log2_diff_max_tt_min_qt_inter_slice ue(v)  76  }  77  if(qtbtt_dual_tree_intra_flag ) {  78  sps_log2_diff_min_qt_min_cb_intra_slice_chroma ue(v)  79  sps_max_mtt_hierarchy_depth_intra_slice_chroma ue(v)  80   if(sps_max_mtt_hierarchy_depth_intra_slice_chroma != 0 ) {  81   sps_log2_diff_max_bt_min_qt_intra_slice_chroma ue(v)  82   sps_log2_diff_max_tt_min_qt_intra_slice_chroma ue(v)  83   }  84  } 85  sps_max_luma_transform_size_64_flag u(1)    86 ** sps_joint_cbcr_enabled_flag u(1)  87  if( ChromaArrayType != 0 ) {  88  same_qp_table_for_chroma u(1)  89   numQpTables =same_qp_table_for_chroma ? 1 : ( sps_joint_cbcr_enabled_flag ? 3 : 2) 90   for( i = 0; i < numQpTables; i++ ) {  91   qp_table_start_minus26[ i ] se(v)  92   num_points_in_qp_table_minus1[ i ] ue(v)  93    for( j = 0; j <=num_points_in_qp_table_minus1[ i ]; j++ ) {  94    delta_qp_in_val_minus1[ i ][ j ] ue(v)  95     delta_qp_diff_val[ i][ j ] ue(v)  96    }  97   }  98  }  99  sps_sao_enabled_flag u(1) 100 sps_alf_enabled_flag u(1) 101  sps_transform_skip_enabled_flag u(1) 102 if( sps_transform_skip_enabled_flag ) 103   sps_bdpcm_enabled_flag u(1)  104 **  if( sps_bdpcm_enabled_flag && chroma_format_idc = = 3 )   105**   sps_bdpcm_chroma_enabled_flag u(1) 106 sps_ref_wraparound_enabled_flag u(1) 107  if(sps_ref_wraparound_enabled_flag ) 108   sps_ref_wraparound_offset_minus1ue(v) 109  sps_temporal_mvp_enabled_flag u(1) 110  if(sps_temporal_mvp_enabled_flag ) 111   sps_sbtmvp_enabled_flag u(1) 112 sps_amvr_enabled_flag u(1) 113  sps_bdof_enabled_flag u(1) 114  if(sps_bdof_enabled_flag ) 115   sps_bdof_pic_present_flag u(1) 116 sps_smvd_enabled_flag u(1) 117  sps_dmvr_enabled_flag u(1) 118  if(sps_dmvr_enabled_flag) 119   sps_dmvr_pic_present_flag u(1) 120 sps_mmvd_enabled_flag u(1) 121  sps_isp_enabled_flag u(1) 122 sps_mrl_enabled_flag u(1) 123  sps_mip_enabled_flag u(1) 124  if(ChromaArrayType != 0 ) 125   sps_cclm_enabled_flag u(1) 126   if(sps_cclm_enabled_flag && chroma_format_idc = = 1 ) [Ed. (JC): shouldsps_cclm_colocated_chroma_flag also be signalled for 422 case since it’sused in the decoding process, to be confirmed] 127  sps_cclm_colocated_chroma_flag u(1) 128  sps_mts_enabled_flag u(1) 129 if( sps_mts_enabled flag ) { 130   sps_explicit_mts_intra_enabled_flagu(1) 131   sps_explicit_mts_inter_enabled_flag u(1) 132  } 133 sps_sbt_enabled _flag u(1) 134  sps_affine_enabled_flag u(1) 135  if(sps_affine_enabled_flag ) { 136   sps_affine_type_flag u(1) 137  sps_affine_amvr_enabled_flag u(1) 138   sps_affine_prof_enabled_flagu(1) 139   if( sps_affine_prof_enabled_flag ) 140   sps_prof_pic_present_flag u(1) 141  }   142 **  if( chroma_format_idc= = 3 ) { 143   sps_palette_enabled_flag u(1)   144 **  sps_act_enabled_flag u(1) 145  } 146  sps_bcw_enabled_flag u(1) 147 sps_ibc_enabled_flag u(1) 148  sps_ciip_enabled_flag u(1) 149  if(sps_mmvd_enabled_flag ) 150   sps_fpel_mmvd_enabled_flag u(1) 151 sps_triangle_enabled_flag u(1) 152  sps_lmcs_enabled_flag u(1) 153 sps_lfnst_enabled_flag u(1) 154  sps_ladf_enabled_flag u(1) 155  if(sps_ladf_enabled_flag ) { 156   sps_num_ladf_intervals_minus2 u(2) 157  sps_ladf_lowest_interval_qp_offset se(v) 158   for( i = 0; i <sps_num_ladf_intervals_minus2 + 1; i++ ) { 159    sps_ladf_qp_offset[ i] se(v) 160    sps_ladf_delta_threshold_minus1[ i ] ue(v) 161   } 162  }163  sps_scaling_list_enabled_flag u(1) 164 sps_loop_filter_across_virtual_boundaries_disabled_present_flag u(1)165  if( sps_loop_filter_across_virtual_boundaries_disabled_present_flag) { 166   sps_num_ver_virtual_boundaries u(2) 167   for( i = 0; i <sps_num_ver_virtual_boundaries; i++ ) 168   sps_virtual_boundaries_pos_x[ i ] u(13) 169  sps_num_hor_virtual_boundaries u(2) 170   for( i = 0; i <sps_num_hor_virtual_boundaries; i++) 171   sps_virtual_boundaries_pos_y[ i ] u(13) 172  } 173  if(sps_ptl_dpb_hrd_params_present_flag { 174  sps_general_hrd_params_present_flag u(1) 175   if(sps_gencral_hrd_params_present_flag ) { 176    general_hrd_parameters( )177    if( sps_max_sub_layers_minus1 > 0 ) 178    sps_sub_layer_cpb_params_present_flag u(1) 179    firstSubLayer =sps_sub_layer_cpb_params_present_flag ? 0 :     sps_max_sub_layers_minus1 180    ols_hrd_parameters( firstSubLayer, sps_max_sub_layers_minus1 ) 181   } 182  } 183 vui_parameters_present_flag u(1) 184  if( vui_parameters_present_flag )185   vui_parameters( ) 186  sps_extension_flag u(1) 187  if(sps_extension_flag ) 188   while( more_rbsp_data( ) ) 189   sps_extension_data_flag u(1) 190  rbsp_trailing_bits( ) 191 }

III. Disabling Coding Tools Inapplicable to Monochrome Video or Videowith Separately Coded Components

In some embodiments, to support the coding of monochrome video and theseparate coding of three color components of, for example, a 4:4:4chroma format video, a variable indicating a chroma array type isdefined. The variable is denoted by ChromaArrayType. The variableChromaArrayType can be used to disable the coding tools that are notapplicable when the video is monochrome and when the color components ofthe video are required to be encoded separately and independently.Depending on the value of separate_colour_plane_flag, the value of thevariable ChromaArrayType can be assigned as follows:

-   -   If separate_colour_plane_flag is equal to 0, ChromaArrayType is        set equal to chroma_format_idc (e.g., 0, 1, 2, or 3).    -   Otherwise (separate_colour_plane_flag is equal to 1),        ChromaArrayType is set equal to 0.        When ChromaArrayType is 0, the coding tools enabled by        sps_joint_cbcr_enabled_flag, sps_act_enabled_flag,        sps_bdpcm_chroma_enabled_flag, or the like can be disabled.

Table 3 shows a modified version of the SPS syntax shown in Table 2. Atrows 84-85 of Table 3, sps_joint_cbcr_enabled_flag is signaled whenChromaArrayType has a non-zero value. When ChromaArrayType equals zero,which indicates a current video referring the SPS of Table 2 ismonochrome, or includes separately encoded components,sps_joint_cbcr_enabled_flag is not signaled, and can be inferred to beequal to zero. Accordingly, the joint coding of chroma residuals can bedisabled. Compared with the Table 2 examples, semantics ofsps_joint_cbcr_enabled_flag can be modified as follows:sps_joint_cbcr_enabled_flag equal to 0 specifies that the joint codingof chroma residuals is disabled. sps_joint_cbcr_enabled_flag equal to 1specifies that the joint coding of chroma residuals is enabled. Whensps_joint_cbcr_enabled_flag is not present, it is inferred to be beequal to 0.

At rows 102-103 of Table 3, sps_bdpcm_chroma_enabled_flag is signaledwhen BDPCM is enabled and ChromaArrayType has a non-zero value. WhenChromaArrayType equals zero, sps_bdpcm_chroma_enabled_flag is notsignaled, and can be inferred to be equal to zero. Accordingly, theBDPCM for chroma can be disabled. Semantics ofsps_bdpcm_chroma_enabled_flag can be the same as in the Table 2 example.

At rows 140, 142, and 143 of Table 3, sps_act_enabled_flag is signaledwhen the video has a 4:4:4 chroma format and ChromaArrayType has anon-zero value. When ChromaArrayType equals zero, sps_act_enabled_flagis not signaled, and can be inferred to be equal to zero. Accordingly,the ACT can be disabled. Semantics of sps_act_enabled_flag can be thesame as in the Table 2 example.

TABLE 3 Descriptor  1 sps_parameter_set_rbsp( ) {  2 sps_decoding_parameter_set_id u(4)  3  sps_video_parameter_set_id u(4) 4  sps_max_sub_layers_minus1 u(3)  5  sps_reserved_zero_4bits u(4)  6 sps_ptl_dpb_hrd_params_present_flag u(1)  7  if(sps_dpb_hrd_params_present_flag )  8   profile_tier_level( 1,sps_max_sub_layers_minus1 )  9  gdr_enabled_flag u(1)  10 sps_seq_parameter_set_id u(4)    11 **  chroma_format_idc u(2)    12 ** if( chroma_format_idc = = 3)    13 **   separate_colour_plane_flag u(1) 14  ref_pic_resampling_enabled_flag u(1)  15 pic_width_max_in_luma_samples ue(v)  16  pic_height_max_in_luma_samplesue(v)  17  sps_log2_ctu_size_minus5 u(2)  18  subpics_present_flag u(1) 19   sps_num_subpics_minus1 u(8)  20   for( i = 0; i <=sps_num_subpics_minus1; i++ ) {  21    subpic_ctu_top_left_x[ i ] u(v) 22    subpic_ctu_top_left_y[ i ] u(v)  23    subpic_width_minus1[ i ]u(v)  24    subpic_height_minus1[ i ] u(v)  25   subpic_treated_as_pic_flag[ i ] u(1)  26   loop_filter_across_subpic_enabled_flag[ i ] u(1)  27   }  28  }  29 sps_subpic_id_present_flag u(1)  30  if( sps_subpics_id_present_flag ){  31   sps_subpic_id_signalling_present_flag u(1)  32   if(sps_subpics_id_signalling_present_flag ) {  33   sps_subpic_id_len_minus1 ue(v)  34    for( i = 0; i <=sps_num_subpics_minus1; i++ )  35     sps_subpic_id[ i ] u(v)  36   } 37  }  38  bit_depth_minus8 ue(v)  39  min_qp_prime_ts_minus4 ue(v)  40 sps_weighted_pred_flag u(1)  41  sps_weighted_bipred_flag u(1)  42 log2_max_pic_order_cnt_lsb_minus4 u(4)  43  sps_poc_msb_flag u(1)  44 if( sps_poc_msb_flag )  45   poc_msb_len_minus1 ue(v)  46  if(sps_max_sub_layers_minus1 > 0 )  47   sps_sub_layer_dpb_params_flag u(1) 48  if( sps_ptl_dpb_hrd_params_present_flag )  49   dpb_parameters( 0,sps_max_sub_layers_minus1, sps_sub_layer_dpb_params_flag )  50 long_term_ref_pics_flag u(1)  51  inter_layer_ref_pics_present_flagu(1)  52  sps_idr_rpl_present_flag u(1)  53  rpl1_same_as_rpl0_flag u(1) 54  for( i = 0; i < !rpl1_same_as_rpl0_flag ? 2: 1; i++ ) {  55  num_ref_pic_lists_in_sps[ i ] ue(v)  56   for( j = 0; j <num_ref_pic_lists_in_sps[ i ]; j++)  57    ref_pic_list_struct( i, j ) 58  }  59  if( ChromaArrayType != 0 )  60   qtbtt_dual_tree_intra_flagu(1)  61  log2_min_luma_coding_block_size_minus2 ue(v)  62 partition_constraints_override_enabled_flag u(1)  63 sps_log2_diff_min_qt_min_cb_intra_slice_luma ue(v)  64 sps_log2_diff_min_qt_min_cb_inter_slice ue(v)  65 sps_max_mtt_hierarchy_depth_inter_slice ue(v)  66 sps_max_mtt_hierarchy_depth_intra_slice_luma ue(v)  67  if(sps_max_mtt_hierarchy_depth_intra_slice_luma != 0 ) {  68  sps_log2_diff_max_bt_min_qt_intra_slice_luma ue(v)  69  sps_log2_diff_max_tt_min_qt_intra_slice_luma ue(v)  70  }  71  if(sps_max_mtt_hierarchy_depth_inter_slice != 0 ) {  72  sps_log2_diff_max_bt_min_qt_inter_slice ue(v)  73  sps_log2_diff_max_tt_min_qt_inter_slice ue(v)  74  }  75  if(qtbtt_dual_tree_intra_flag ) {  76  sps_log2_diff_min_qt_min_cb_intra_slice_chroma ue(v)  77  sps_max_mtt_hierarchy_depth_intra_slice_chroma ue(v)  78   if(sps_max_mtt_hierarchy_depth_intra_slice_chroma != 0 ) {  79   sps_log2_diff max_bt_min_qt_intra_slice_chroma ue(v)  80   sps_log2_diff_max_tt_min_qt_intra_slice_chroma ue(v)  81   }  82  } 83  sps_max_luma_transform_size_64_flag u(1)    84 **  if(ChromaArrayType != 0 ) { u(1)    85 **  sps_joint_cbcr_enabled_flag  86  same_qp_table_for_chroma u(1)  87   numQpTables =same_qp_table_for_chroma ? 1 : ( sps_joint_cbcr_enabled_ flag ? 3 : 2 ) 88   for( i = 0; i < numQpTables; i++ ) {  89   qp_table_start_minus26[ i ] se(v)  90   num_points_in_qp_table_minus1[ i ] ue(v)  91    for( j = 0; j <=num_points_in_qp_table_minus1[ i ]; j++ ) {  92    delta_qp_in_val_minus1[ i ][ j ] ue(v)  93     delta_qp_diff_val[ i][ j ] ue(v)  94    }  95   }  96  }  97  sps_sao_enabled_flag u(1)  98 sps_alf_enabled_flag u(1)  99  sps_transform_skip_enabled_flag u(1) 100 if( sps_transfonn_skip_criabled_flag ) 101   sps_bdpcm_enabled_flagu(1)   102 **  if( sps_bdpcm_enabled_flag && ChromaArrayType!=0)   103**   sps_bdpcm_chroma_enabled_flag u(1) 104 sps_ref_wraparound_enabled_flag u(1) 105  if(sps_ref_wraparound_enabled_flag ) 106   sps_ref_wraparound_offset_minus1ue(v) 107  sps_temporal_mvp_enabled_flag u(1) 108  if(sps_temporal_mvp_enabled_flag ) 109   sps_sbtmvp_enabled_flag u(1) 110 sps_amvr_enabled_flag u(1) 111  sps_bdof_enabled_flag u(1) 112  if(sps_bdof_enabled_flag ) 113   sps_bdof_pic_present_flag u(1) 114 sps_smvd_enabled_flag u(1) 115  sps_dmvr_enabled_flag u(1) 116  if(sps_dmvr_enabled_flag) 117   sps_dmvr_pic_present_flag u(1) 118 sps_mmvd_enabled_flag u(1) 119  sps_isp_enabled_flag u(1) 120 sps_mrl_enabled_flag u(1) 121  sps_mip_enabled_flag u(1) 122  if(ChromaArrayType != 0 ) 123   sps_cclm_enabled_flag u(1) 124   if(sps_cclm_enabled_flag && chroma_format_idc = = 1 ) [Ed. (JC): shouldsps_cclm_colocated_chroma_flag also be signalled for 422 case since it’sused in the decoding process, to be confirmed] 125  sps_cclm_colocated_chroma_flag u(1) 126  sps_mts_enabled_flag u(1) 127 if( sps_mts_enabled flag ) { 128   sps_explicit_mts_intra_enabled_flagu(1) 129   sps_explicit_mts_inter_enabled_flag u(1) 130  } 131 sps_sbt_enabled _flag u(1) 132  sps_affine_enabled_flag u(1) 133  if(sps_affine_enabled_flag ) { 134   sps_affine_type_flag u(1) 135  sps_affine_amvr_enabled_flag u(1) 136   sps_affine_prof_enabled_flagu(1) 137   if( sps_affine_prof_enabled_flag ) 138   sps_prof_pic_present_flag u(1) 139  }   140 **  if( chroma_format_idc= = 3 ) { 141   sps_palette_enabled_flag u(1)   142 **   if( ChromaArrayType != 0 )   143 **   sps_act_enabled_flag u(1) 144  } 145 sps_bcw_enabled_flag u(1) 146  sps_ibc_enabled_flag u(1) 147 sps_ciip_enabled_flag u(1) 148  if( sps_mmvd_enabled_flag ) 149  sps_fpel_mmvd_enabled_flag u(1) 150  sps_triangle_enabled_flag u(1)151  sps_lmcs_enabled_flag u(1) 152  sps_lfnst_enabled_flag u(1) 153 sps_ladf_enabled_flag u(1) 154  if( sps_ladf_enabled_flag ) { 155  sps_num_ladf_intervals_minus2 u(2) 156  sps_ladf_lowest_interval_qp_offset se(v) 157   for( i = 0; i <sps_num_ladf_intervals_minus2 + 1; i++ ) { 158    sps_ladf_qp_offset[ i] se(v) 159    sps_ladf_delta_threshold_minus1[ i ] ue(v) 160   } 161  }162  sps_scaling_list_enabled_flag u(1) 163 sps_loop_filter_across_virtual_boundaries_disabled_present_flag u(1)164  if( sps_loop_filter_across_virtual_boundaries_disabled_present_flag) { 165   sps_num_ver_virtual_boundaries u(2) 166   for( i = 0; i <sps_num_ver_virtual_boundaries; i++ ) 167   sps_virtual_boundaries_pos_x[ i ] u(13) 168  sps_num_hor_virtual_boundaries u(2) 169   for( i = 0; i <sps_num_hor_virtual_boundaries; i++) 170   sps_virtual_boundaries_pos_y[ i ] u(13) 171  } 172  if(sps_ptl_dpb_hrd_params_present_flag { 173  sps_general_hrd_params_present_flag u(1) 174   if(sps_general_hrd_params_present_flag ) { 175    general_hrd_parameters( )176    if( sps_max_sub_layers_minus1 > 0 ) 177    sps_sub_layer_cpb_params_present_flag u(1) 178    firstSubLayer =sps_sub_layer_cpb_params_presentilag ? 0 :     sps_max_sub_layers_minus1 179    ols_hrd_parameters( firstSubLayer, sps_max_sub_layers_minus1 ) 180   } 181  } 182 vui_parameters_present_flag u(1) 183  if( vui_parameters_prcsent_flag )184   vui_parameters( ) 185  sps_extension_flag u(1) 186  if(sps_extension_flag ) 187   while( more_rbsp_data( ) ) 188   sps_extension_data_flag u(1) 189  rbsp_trailing_bits( ) 190 }

In some embodiments, alternate implementations are employed fordisabling coding tools inapplicable to a monochrome video or a videoincluding separately encoded components.

In an embodiment, the following syntax of sps_act_enabled_flag in Table4 (which is copied from Table 3) can be expressed with alternate syntaxshown in Table 5 to set the value of sps_act_enabled_flag to 0 whenchroma_format_idc equals 3 and ChromaArrayType is zero. Sincechroma_format_idc==3 and separate_colour_plan_flag==0 impliesChromaArrayType not 0, the syntax in Table 4 and Table 5 can have thesame effect. It is noted that the signaling of sps_act_enabled_flag isindependent from the signaling of sps_palette_enabled_flag at row 141.

TABLE 4 140 ** if( chroma_format_idc = = 3 ) { 141   sps_palette_enabled_flag u(1) 142 **  if( ChromaArrayType != 0 ) 143 **  sps_act_enabled_flag u(1) 144   }

TABLE 5 140 ** if( chroma_format_idc = = 3 ) { 141   sps_palette_enabled_flag u(1) 142 **  if(separate_colour_plane_flag==0) 143 **   sps_act_enabled_flag u(1) 144   }

In an embodiment, the following syntax of sps_bdpcm_chroma_enabled_flagin Table 6 (which is copied from Table 3) can be expressed withalternate syntax as shown in Table 7 to set the value ofsps_bdpcm_chroma_enabled_flag to 0 when ChromaArrayType is zero. InTable 7, the value of sps_bdpcm_chroma_enabled_flag is inferred to be 0when ChromaArrayType is zero or a sps_transquant_bypass_flag to supportBDPCM for lossless equals 0. When sps_tranquant_bypass_flag equals 1,sps_transquant_bypass_flag indicates that transformation andquantization pass shall be activated at the CU level. Otherwise, ifsps_tranquant_bypass_flag equals 0, transformation and quantizationbypass shall not be activated. The sps_tranquant_bypass_flag can besignaled at the SPS or be inferred to be 1 for lossless coding asindicated by other SPS level lossless coding indication flag.

TABLE 6 102 ** if( sps_bdpcm_enabled_flag && ChromaArrayType!=0) 103 ** sps_bdpcm_chroma_enabled_flag u(1)

TABLE 7 102 **  if( sps_bdpcm_enabled_flag && cu_transquant_bypass_ flag&&ChromaArrayType!=0) 103 **   sps_bdpcm_chroma_enabled_flag u(1)

In an embodiment, the syntax in Table 7 is used. However, different fromthe above embodiment, the semantics of the syntax elementsps_tranquant_bypass_flag is defined as follows. Whensps_tranquant_bypass_flag equals 1, sps_transquant_bypass_flag indicatesthat transformation and quantization pass may (instead of shall) beactivated at the CU level. Otherwise, if sps_tranquant_bypass_flagequals 0, transformation and quantization bypass shall not be activated.The sps_tranquant_bypass_flag can be signaled at the SPS or be inferredto be 1 for lossless coding as indicated by other SPS level losslesscoding indication flag.

FIG. 8 shows an example process (800) of receiving flags of crosscomponent coding tools or chroma component based coding tools in abitstream of a coded video. The process (800) can be performed at adecoder. The process (800) can start from (S801) and proceed to (S810).

At S(810), a syntax element can be received in the bitstream thatindicate whether pictures of a sequence each are monochrome or haveseparately encoded components. For example, the syntax element can bethe chroma_format_idc, or the separate_color_plane_flag. Thechroma_format_idc being 0 can indicate the pictures are monochrome. Theseparate_color_plane_flag being 1 can indicate the pictures each havingseparately coded components. In both the cases, the ChromaArrayType canhave a value of 0.

As an example, the sequence of pictures refer the SPS in Table 3. Thechroma_format_idc signaled in row 11 in Table 3 is received. When thechroma_format_idc has a value of 0, it can be determined the picturesare monochrome. When the chroma_format_idc equals zero, theseparate_color_plane_flag may not be signaled at row 13, and can beinferred to be equal to zero in one example. Accordingly, theChromaArrayType can be set equal to chroma_format_idc that is zero forthe current case.

When the chroma_format_idc has a value of 3 indicating a 4:4:4 chromaformat of the pictures of the sequence, the separate_colour_plane_flagcan be received at row 13. If the separate_colour_plane_flag has a valueof 1, which indicates the pictures are required to separately coding thecomponents, it can be determined the pictures have separately encodedcomponents. The ChromaArrayType can be set equal to zero.

In other cases, when the chroma_format_idc received in row 11 has avalue of 1 or 2, or when the chroma_format_idc received in row 11 has avalue of 3 but the separate_colour_plane_flag has a value of 0, it canbe determined the pictures each are not monochrome and includecomponents that are not coded separately. Joint components coding toolsor chroma based coding tools can be applied to the pictures. For thechroma_format_idc received in row 11 of Table 3 having a value of 1 or 2(the pictures are not monochrome), the separate_colour_plane_flag can beinferred as zero. Accordingly, the ChromeArrayType can take the value ofchroma_format_idc that is 1 or 2 (not zero). For the scenario that thechroma_format_idc received has a value of 3 but theseparate_colour_plane_flag has a value of 0, the ChromeArrayType canstill take the value of chroma_format_idc that is 3 (not zero).

When the pictures are determined to be monochrome or include separatelyencoded components, or the ChromaArrayType is determined to be equal tozero, the steps of (S820) to (S840) can be performed. The syntaxelements for control of the joint-components coding tools orchroma-based coding tool can be inferred to be equal to zero to disablethose coding tools. Specifically, sps_joint_cbcr_enabled_flag,sps_bdpcm_chroma_enabled_flag, and sps_act_enabled_flag are eachinferred to be equal to zero.

When the pictures are determined to not be monochrome and includecomponents that are not separately encoded, or the chromeArrayType isdetermined to be not equal zero, the steps of (S850) to (S870) can beperformed. The syntax elements for control of the joint-componentscoding tools or chroma-based coding tool can be received from thebitstream. Specifically, sps_joint_cbcr_enabled_flag,sps_bdpcm_chroma_enabled_flag, and sps_act_enabled_flag can be receivedsuccessively.

After either (S840) or (S870), the process (800) can proceed to (S899)and terminate at (S899).

FIG. 9 shows a process (900) of disabling coding tools inapplicable to amonochrome video or a video including separately encoded componentsaccording to an embodiment of the disclosure. The process (900) can beperformed at a decoder such as decoder (710). The process (900) canstart from (S901) and proceed to (S910).

At (S910), a syntax element can be received in a bitstream that indicatewhether a sequence of pictures each are monochrome or have separatelyencoded components. For example, the syntax element can be thechroma_format_idc, or the separate_color_plane_flag in the Table 3example. The chroma_format_idc being 0 can indicate the pictures aremonochrome. The separate_color_plane_flag being 1 can indicate thepictures each having separately coded components. In both the cases(chroma_format_idc being 0 or separate_color_plane_flag being 1), thevariable ChromaArrayType can have a value of 0.

When it is determined the sequence of pictures each are monochrome orhave separately encoded components, the steps (S920) and (S930) can beperformed. At (S920), coding tools that use multiple components of thepictures as input can be disabled, for example, by inferring a value ofa syntax element controlling each corresponding coding tool. Examples ofsuch coding tools can include ACT, joint coding of chroma residuals, orthe like.

At (S930), coding tools that depend on a chroma component of thepictures can be disabled, for example, by inferring a value of a syntaxelement controlling each corresponding coding tool. Examples of suchcoding tools can include BDPCM for chroma. The process (900) can thenproceed to (S999) and terminate at (S999).

When it is determined at (S910) that the sequence of pictures each arenot monochrome or do not have separately encoded components, the step(S940) can be performed. At (S940), syntax elements for enabling thejoint component coding tools or chroma component based coding tools canbe received from the bit stream. Whether the syntax elements forenabling those coding tools are signaled in the bitstream may dependingon other conditions or other syntax elements transmitted in thebitstream. The process (900) can then proceed to (S999) and terminate at(S999).

IV. Computer System

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 10 shows a computersystem (1000) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GM's), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 10 for computer system (1000) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1000).

Computer system (1000) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1001), mouse (1002), trackpad (1003), touchscreen (1010), data-glove (not shown), joystick (1005), microphone(1006), scanner (1007), camera (1008).

Computer system (1000) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1010), data-glove (not shown), or joystick (1005), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1009), headphones(not depicted)), visual output devices (such as screens (1010) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1000) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1020) with CD/DVD or the like media (1021), thumb-drive (1022),removable hard drive or solid state drive (1023), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1000) can also include an interface (1054) to one ormore communication networks (1055). Networks can for example bewireless, wireline, optical. Networks can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of networks include local area networks such asEthernet, wireless LANs, cellular networks to include GSM, 3G, 4G, 5G,LTE and the like, TV wireline or wireless wide area digital networks toinclude cable TV, satellite TV, and terrestrial broadcast TV, vehicularand industrial to include CANBus, and so forth. Certain networkscommonly require external network interface adapters that attached tocertain general purpose data ports or peripheral buses (1049) (such as,for example USB ports of the computer system (1000)); others arecommonly integrated into the core of the computer system (1000) byattachment to a system bus as described below (for example Ethernetinterface into a PC computer system or cellular network interface into asmartphone computer system). Using any of these networks, computersystem (1000) can communicate with other entities. Such communicationcan be uni-directional, receive only (for example, broadcast TV),uni-directional send-only (for example CANbus to certain CANbusdevices), or bi-directional, for example to other computer systems usinglocal or wide area digital networks. Certain protocols and protocolstacks can be used on each of those networks and network interfaces asdescribed above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1040) of thecomputer system (1000).

The core (1040) can include one or more Central Processing Units (CPU)(1041), Graphics Processing Units (GPU) (1042), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1043), hardware accelerators for certain tasks (1044), graphicsadapters (1050), and so forth. These devices, along with Read-onlymemory (ROM) (1045), Random-access memory (1046), internal mass storagesuch as internal non-user accessible hard drives, SSDs, and the like(1047), may be connected through a system bus (1048). In some computersystems, the system bus (1048) can be accessible in the form of one ormore physical plugs to enable extensions by additional CPUs, GPU, andthe like. The peripheral devices can be attached either directly to thecore's system bus (1048), or through a peripheral bus (1049). In anexample, the screen (˜˜x10) can be connected to the graphics adapter(˜˜x50). Architectures for a peripheral bus include PCI, USB, and thelike.

CPUs (1041), GPUs (1042), FPGAs (1043), and accelerators (1044) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1045) or RAM (1046). Transitional data can also be stored in RAM(1046), whereas permanent data can be stored for example, in theinternal mass storage (1047). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1041), GPU (1042), massstorage (1047), ROM (1045), RAM (1046), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1000), and specifically the core (1040) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1040) that are of non-transitorynature, such as core-internal mass storage (1047) or ROM (1045). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1040). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1040) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1046) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1044)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

-   VTM: Versatile Video Coding Test Model-   SPS: sequence parameter set-   BDPCM: Block-based Delta Pulse Code Modulation-   ACT: Adaptive Colour Transform-   JEM: joint exploration model-   VVC: versatile video coding-   BMS: benchmark set-   MV: Motion Vector-   HEVC: High Efficiency Video Coding-   SEI: Supplementary Enhancement Information-   VUI: Video Usability Information-   GOPs: Groups of Pictures-   TUs: Transform Units,-   PUs: Prediction Units-   CTUs: Coding Tree Units-   CTBs: Coding Tree Blocks-   PBs: Prediction Blocks-   HRD: Hypothetical Reference Decoder-   SNR: Signal Noise Ratio-   CPUs: Central Processing Units-   GPUs: Graphics Processing Units-   CRT: Cathode Ray Tube-   LCD: Liquid-Crystal Display-   OLED: Organic Light-Emitting Diode-   CD: Compact Disc-   DVD: Digital Video Disc-   ROM: Read-Only Memory-   RAM: Random Access Memory-   ASIC: Application-Specific Integrated Circuit-   PLD: Programmable Logic Device-   LAN: Local Area Network-   GSM: Global System for Mobile communications-   LTE: Long-Term Evolution-   CANBus: Controller Area Network Bus-   USB: Universal Serial Bus-   PCI: Peripheral Component Interconnect-   FPGA: Field Programmable Gate Areas-   SSD: solid-state drive-   IC: Integrated Circuit-   CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method of video decoding performed in a videodecoder, comprising: receiving a first syntax element from a bitstreamof a coded video, the first syntax element indicating whether a sequenceof pictures are monochrome or include three color components that arecoded separately; and inferring a value of a second syntax element todisable a coding tool that uses multiple color components of a pictureas input or depends on a chroma component of a picture based on thefirst syntax element indicating that the sequence of pictures includethree color components that are coded separately, wherein the inferredvalue of the second syntax element indicates active color transform(ACT) is disabled.
 2. The method of claim 1, wherein the value of thesecond syntax element is in a sequence parameter set (SPS).
 3. Themethod of claim 1, wherein the inferring the value of the second syntaxelement comprises: determining a value of a variable to be zero based onthe first syntax element indicating that the sequence of pictures aremonochrome or include three color components that are coded separately,the variable indicating a chroma array type of the sequence of pictures;and in response to determining the value of the variable to be zero,inferring the value of the second syntax element to be equal to zero. 4.The method of claim 1, further comprising: receiving the second syntaxelement indicating whether the ACT is enabled from the bitstream of thecoded video based on the sequence of pictures being determined toinclude three color components that are coded separately.
 5. The methodof claim 1, further comprising: determining a value of a variableindicating a chroma array type of the sequence of pictures based on thesequence of pictures being determined as not monochrome and includethree color components that are not coded separately; and receiving thesecond syntax element indicating whether the ACT is enabled from thebitstream of the coded video based on the value of the variable beingdetermined to be non-zero.
 6. The method of claim 2, wherein the secondsyntax element is chroma_format_idc.
 7. The method of claim 6, whereinthe value of the second syntax element indicates that the sequence ofpictures has separately encoded color components.
 8. An apparatus ofvideo decoding, comprising: circuitry configured to: receive a firstsyntax element from a bitstream of a coded video, the first syntaxelement indicating whether a sequence of pictures are monochrome orinclude three color components that are coded separately; and infer avalue of a second syntax element to disable a coding tool that usesmultiple color components of a picture as input or depends on a chromacomponent of a picture based on the first syntax element indicating thatthe sequence of pictures include three color components that are codedseparately, wherein the inferred value of the second syntax elementindicates active color transform (ACT) is disabled.
 9. The apparatus ofclaim 8, wherein the value of the second syntax element is in a sequenceparameter set (SPS).
 10. The apparatus of claim 8, wherein the circuitryis further configured to: determine a value of a variable to be zerobased on the first syntax element indicating that the sequence ofpictures are monochrome or include three color components that are codedseparately, the variable indicating a chroma array type of the sequenceof pictures; and in response to determining the value of the variable tobe zero, infer the value of the second syntax element to be equal tozero.
 11. The apparatus of claim 8, wherein the circuitry is furtherconfigured to: receive the second syntax element indicating whether theACT is enabled from the bitstream of the coded video based on thesequence of pictures being determined to include three color componentsthat are coded separately.
 12. The apparatus of claim 8, wherein thecircuitry is further configured to: determine a value of a variableindicating a chroma array type of the sequence of pictures based on thesequence of pictures being determined as not monochrome and includethree color components that are not coded separately; and receive thesecond syntax element indicating whether the ACT is enabled from thebitstream of the coded video based on the value of the variable beingdetermined to be non-zero.
 13. The apparatus of claim 9, wherein thesecond syntax element is chroma_format_idc.
 14. The apparatus of claim13, wherein the value of the second syntax element indicates that thesequence of pictures has separately encoded color components.
 15. Anon-transitory computer-readable medium storing instructions that, whenexecuted by a processor, cause the processor to perform a method ofvideo decoding, the method comprising: receiving a first syntax elementfrom a bitstream of a coded video, the first syntax element indicatingwhether a sequence of pictures are monochrome or include three colorcomponents that are coded separately; and inferring a value of a secondsyntax element to disable a coding tool that uses multiple colorcomponents of a picture as input or depends on a chroma component of apicture based on the first syntax element indicating that the sequenceof pictures include three color components that are coded separately,wherein the inferred value of the second syntax element indicates activecolor transform (ACT) is disabled.
 16. The non-transitorycomputer-readable medium of claim 15, wherein the value of the secondsyntax element is in a sequence parameter set (SPS).
 17. Thenon-transitory computer-readable medium of claim 15, wherein theinferring the value of the second syntax element comprises: determininga value of a variable to be zero based on the first syntax elementindicating that the sequence of pictures are monochrome or include threecolor components that are coded separately, the variable indicating achroma array type of the sequence of pictures; and in response todetermining the value of the variable to be zero, inferring the value ofthe second syntax element to be equal to zero.
 18. The non-transitorycomputer-readable medium of claim 15, wherein the method furthercomprises: receiving the second syntax element indicating whether theACT is enabled from the bitstream of the coded video based on thesequence of pictures being determined to include three color componentsthat are coded separately.
 19. The non-transitory computer-readablemedium of claim 15, wherein the method further comprises: determining avalue of a variable indicating a chroma array type of the sequence ofpictures based on the sequence of pictures being determined as notmonochrome and include three color components that are not codedseparately; and receiving the second syntax element indicating whetherthe ACT is enabled from the bitstream of the coded video based on thevalue of the variable being determined to be non-zero.
 20. Thenon-transitory computer-readable medium of claim 16, wherein the secondsyntax element is chroma_format_idc.